1. Field of the Invention
The present invention relates to a monolithic ceramic electronic component, e.g., a monolithic capacitor, and a mounting structure thereof. In particular, the present invention relates to a monolithic ceramic electronic component, which is mounted with an electrically conductive adhesive, and a mounting structure thereof.
2. Description of the Related Art
Recently, in order to reduce the environmental load, Pb-free solder including no Pb has been used to mount a monolithic ceramic electronic component. However, the melting point of the Pb-free solder is relatively high and, therefore, a treatment at high temperatures is required during soldering. As a result, cracking often occurs in a ceramic element assembly of the ceramic electronic component because of a difference in the thermal expansion coefficient between the ceramic element assembly and an external terminal electrode.
In addition, an electrically conductive adhesive other than solder has been disclosed. For the electrically conductive adhesive used for this type of purpose, a metal filler made from Ag or other suitable is added to a thermosetting resin, e.g., an epoxy resin. The thermosetting temperature of the electrically conductive adhesive is less than the melting point of the Pb-free solder. Therefore, when the electrically conductive adhesive is used to mount a ceramic electronic component, a thermal stress applied to the ceramic element assembly can be reduced. An example of monolithic ceramic electronic components that are compatible with such mounting using electrically conductive adhesive is disclosed in Japanese Unexamined Patent Application Publication No. 2002-203737.
FIG. 13 is a schematic front sectional view showing the structure of a monolithic ceramic electronic component described in Japanese Unexamined Patent Application Publication No. 2002-203737. Here, a monolithic ceramic electronic component 110 includes ceramic sintered body 113 in which first and second internal electrodes 111 and 112 are laminated with ceramic layers therebetween. First and second external electrodes 114 and 115 are arranged so as to cover first and second end surfaces of the ceramic sintered body 113. In the first and the second external electrodes 114 and 115, a first electrode layer 121 and a second electrode layer 122 are laminated. The glass frit content G1 in the first electrode layer 121, the thickness of the first electrode layer 121, the glass frit content G2 in the second electrode layer 122, and the thickness of the second electrode layer 122 are specified to be within specific ranges. Japanese Unexamined Patent Application Publication No. 2002-203737 discloses that the resistance to a stress generated during hardening of the electrically conductive adhesive and a stress due to bending of a substrate during mounting through the use of the electrically conductive adhesive can be improved.
Furthermore, Japanese Unexamined Patent Application Publication No. 9-50935 discloses a monolithic capacitor suitable for uses at medium and high voltages because the voltage at which leakage due to surface flashover in the air begins is increased. Here, first internal electrodes and second internal electrodes are arranged adjacently with ceramic layers therebetween. Each of the first and the second internal electrodes has a relatively wide portion that extends to an end surface of the ceramic sintered body and a relatively narrow portion connected to a front end side of the wide portion. This relatively narrow portion is overlapped with a relatively wide portion of the other internal electrode when the two electrodes are stacked with a ceramic layer therebetween and, thereby, a shielding effect is improved. Consequently, a field strength between the relatively narrow portion of the internal electrode and an external electrode different from the external electrode connected to the internal electrode is reduced.
Recently, as described in Japanese Unexamined Patent Application Publication No. 2002-203737, use of electrically conductive adhesive has been attempted for mounting of the ceramic electronic component. However, in the case in which a ceramic electronic component was mounted on a substrate using an electrically conductive adhesive, in practice, the characteristics of the ceramic electronic component are likely to be deteriorated. That is, even when the characteristics were measured at a ceramic electronic component stage and it was determined that the characteristics were good, when evaluation was performed after the ceramic electronic component was mounted using the electrically conductive adhesive, the characteristics deteriorated in some instances.
In this connection, in the monolithic capacitor described in Japanese Unexamined Patent Application Publication No. 9-50935, the internal electrode has the relatively wide portion and the relatively narrow portion. Therefore, the internal electrode described in Japanese Unexamined Patent Application Publication No. 9-50935 has a shape similar to the shape of the internal electrode according to a preferred embodiment of the present invention. However, Japanese Unexamined Patent Application Publication No. 9-50935 does not recognize or identify a problem when the monolithic ceramic electronic component is mounted using an electrically conductive adhesive.